This is a timeout issue, probably encountered on a slow machine.
Checked in revision 85964 increasing the default timeout to cater to slower machines.
However, I also see that the timeout mechanism used by barrier isn't very robust. I'll submit a patch with a suggested change soon.

FWIW, my snow leopard slave isn't slow at all so I doubt there's a timeout related to machine speed going on here, as its failing thus:
test test_threading failed -- Traceback (most recent call last):
File "/Users/pythonbuildbot/buildarea/3.x.hansen-osx-x86/build/Lib/test/lock_tests.py", line 784, in test_default_timeout
self.run_threads(f)
File "/Users/pythonbuildbot/buildarea/3.x.hansen-osx-x86/build/Lib/test/lock_tests.py", line 615, in run_threads
f()
File "/Users/pythonbuildbot/buildarea/3.x.hansen-osx-x86/build/Lib/test/lock_tests.py", line 783, in f
self.assertRaises(threading.BrokenBarrierError, self.barrier.wait)
AssertionError: BrokenBarrierError not raised by wait
Its actually a really spammy sort of failure with a lot of errors before it, which may or may not shed more light on the situation: http://www.python.org/dev//buildbot/3.x.stable/builders/x86%20Snow%20Leopard%203.x/builds/267/steps/test/logs/stdio
This was r85883, so after the increase in the timeout.